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  Analog/digital conversion method and analog/digital conversion circuitUSPTO Application #: 20060092068Title: Analog/digital conversion method and analog/digital conversion circuit Abstract: Paying attention to the difference between a subsequently inputted analog signal and a reference signal which is an analog signal converted to the digital signal immediately before for instance, changing timing dynamically for converting the analog signal to the digital signal, and converting an analog signal sampled at the timing of changing dynamically to a digital signal. (end of abstract)
Agent: Arent Fox PLLC - Washington, DC, US Inventors: Shunichi Ko, Akihiro Fujitsuka USPTO Applicaton #: 20060092068 - Class: 341155000 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20060092068. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2004-319756, filed in Nov. 2, 2004, the entire contents of which are incorporated herein by reference. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to a technique for sampling an analog signal and converting the sampled analog signal to a digital signal. [0004] 2. Description of the Related Art [0005] A lot of modern electronic equipment is configured to perform a data processing through an analog to digital conversion ("AD conversion" hereinafter) of analog signal to digital signal (i.e., digital value) to control itself. The analog signal is a sensor output for instance. [0006] The analog signal is prone to an influence of noise, wherein influence causes AD conversion of an analog signal to be overlapped with noise. This generally prompts to compute a weighted average as shown by FIG. 1 to figure out the digital signals (i.e., sampling values) within a certain time period. The example shown by FIG. 1 is a case where seven samplings are taken in a certain time period. In FIG. 1, the "converted values" show the digital signal values (i.e., sampling values) gained by converting respective analog signals. The "averages" show the averages calculated from the digital signal values gained by the respective times. In computing the weighted averages, integration by adding a predetermined number (i.e., weighting) respectively to the digital signals (i.e., sampling values) gained by AD conversion alleviates an influence of noise. [0007] A conventional AD conversion circuit has been configured to conduct a plurality of samplings within a certain time period at a predetermined time interval which is usually very small because of being one n-th the time period for obtaining one piece of digital signal. This has caused a problem of heavy load on a data processing apparatus such as CPU for processing a digital signal obtained by such a sampling. [0008] Presently, multiple functions and low costs are in demand for electronic products, increasing the need to make a data processing apparatus, for processing a digital signal, perform other processing in addition to the digital signal processing. Therefore, a further reduction of the load for processing a digital signal is considered very important. Also highly important is to maintain a precision of the processing. [0009] A conventional AD conversion circuit dealing with an analog signal overlapped with noise is the one noted in a Japanese patent laid-open application publication No. 7-210319. The conventional AD conversion circuit noted in the aforementioned publication is equipped with a switch having a terminal for receiving an analog signal and another terminal being connected with the ground on the front end of the AD converter so as to switch the switch in response to the result of detecting noise, thereby preventing an analog signal overlapped with noise from being sampled by connecting the AD converter with ground when a noise is detected. [0010] In the conventional AD conversion circuit noted in the Japanese patent laid-open application publication No. 7-210319, however, a data processing apparatus must be disposed for the processing in dealing with a change of sampling object, because switching the switch changes the sampling object, hence further increasing the load for processing the digital signal. SUMMARY OF THE INVENTION [0011] The purpose of the present invention is to provide a technique for alleviating a load for processing a digital signal obtained by converting an analog signal, while maintaining the accuracy of processing the digital signal. [0012] An AD conversion method of the first aspect of the present invention, assuming to be applied for converting a sampled analog signal to a digital signal, comprises: monitoring a difference between a subsequently inputted analog signal and a reference signal which is an analog signal converted to the digital signal immediately before; and sampling an analog signal inputted at the time when the difference becomes outside a predetermined range and converting the sampled analog signal to a digital signal. [0013] An AD conversion method of the second aspect of the present invention, assuming to be applied for obtaining a digital signal gained by converting a sampled analog signal, comprises: monitoring a difference between either one of subsequently obtained digital signal and analog signal to be converted to the digital signal and a reference signal which is either one of the digital signal obtained immediately before and analog signal converted to the digital signal; and obtaining a digital signal gained by converting an analog signal inputted at the time when the difference becomes outside a predetermined range. [0014] An AD conversion method of the third aspect of the present invention, assuming to be applied for converting a sampled analog signal to a digital signal, comprises: changing timing dynamically for converting the analog signal to the digital signal by paying attention to a momentary change of the analog signal, and sampling the analog signal at the timing of changing dynamically and converting the sampled analog signal to the digital signal. [0015] An AD conversion circuit of the first aspect of the present invention, assuming to be applied for converting a sampled analog signal to a digital signal, comprises an AD conversion unit for converting the sampled analog signal to a digital value, a signal retention unit for retaining an analog signal converted by the AD conversion unit immediately before, a comparator unit for comparing the analog signal retained by the signal retention unit with a subsequently inputted analog signal, and a management unit for making the AD conversion unit convert an analog signal inputted at the time when a difference between analog signals compared by the comparator unit becomes outside a predetermined range to a digital signal and making the signal retention unit retain the analog signal. [0016] An AD conversion circuit of the second aspect of the present invention, assuming to be applied for converting a sampled analog signal to a digital signal, comprises a timing determination unit for determining timing dynamically for converting the analog signal to the digital signal by paying attention to a momentary change of the analog signal, and an AD conversion unit for sampling the analog signal according to the timing determined dynamically by the timing determination unit and converting the sampled analog signal to a digital value. [0017] An AD conversion circuit of the third aspect of the present invention, in addition to the comprisal of the above described first or second aspects thereof, further comprises a time measurement unit for measuring a time interval between the time when said AD conversion unit converts to said digital signal and the next time when the AD conversion unit does the same. [0018] An AD conversion circuit of the fourth aspect of the present invention, in addition to the comprisal of the above described first or second aspects thereof, further comprises a signal obtainment unit for obtaining the digital signal, an information obtainment unit for obtaining time information indicating a time interval between the time when the signal obtainment unit obtains the digital signal and the next time when the signal obtainment unit obtains a digital signal, and a value calculation unit for calculating a digital signal value in a predetermined time period by using the digital signal obtained by the signal obtainment unit and the time information obtained by the information obtainment unit. [0019] The present invention, by paying attention to a momentary change of analog signal, pays attention to the difference between a subsequently inputted analog signal and a reference signal which is an analog signal converted to a digital signal immediately before for instance, changes timing dynamically for converting an analog signal to a digital signal, and converts the analog signal sampled at the time of changing timing dynamically to the digital signal. [0020] Changing the timing dynamically makes it possible to obtain a required digital signal at a required time. It is possible to avoid an obtainment when there is no, or low, need to obtain a digital signal. This enables a load for digital signal processing to be alleviated while maintaining an accuracy thereof gained by converting an analog signal. BRIEF DESCRIPTION OF THE DRAWINGS Continue reading... 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